In recent years, liquid crystal display units for displaying visible information have come into widespread use for electronic equipment such as navigation systems, televisions, palm-top computers, electronic organizers and portable telephones. In general, these liquid crystal display units are constructed such that a liquid crystal driving IC, i.e., a semiconductor device, is connected to a liquid crystal panel and incidental parts such as a back light and a casing are mounted on the liquid crystal panel. This liquid crystal panel is commonly made in a manner that a liquid crystal is put in between at least two substrates for the liquid crystal, and a polarizing plate, a color filter and others are mounted when necessary.
Many kind of ways of the connection of the liquid crystal driving IC to the liquid crystal panel have been considered, for example, connecting methods based upon a COB (Chip On Board) method, a COG (Chip On Glass) method or the like. According to the COB method, the liquid crystal driving IC is joined through the use of an ACF (Anisotropic Conductive Film) or other joining materials to an insulating substrate having a wiring pattern thereon, and that insulating substrate is connected through a heat seal or the like to the liquid crystal panel.
On the other hand, according to the COG method, the liquid crystal driving IC is directly joined through the use of the ACF or the like to a glass substrate having electrode terminals. In both the COB method and the COG method, a semiconductor device such as the liquid crystal driving IC is connected onto the substrate such as the insulating substrate and the liquid crystal glass substrate.
In the above-mentioned prior connecting methods, the ACF or other joining materials are uniformly placed in between the substrate and the liquid crystal driving IC without making a space therein. For this reason, when the liquid crystal driving IC is joined thereto under pressure, warps take place on the IC itself, or when the liquid crystal driving IC and/or the substrate deform due to the variation of temperature, excessive stresses occur at the bump portions of the liquid crystal driving IC in direct contact with the electrodes on the substrate. As a result, the electrical connecting conditions can become unstable. In addition, for avoiding such problems, the pressure-joining conditions for the liquid crystal driving IC are required to be severely managed within a small tolerance. As a result, a complicated process management is demanded.
Moreover, in the Japanese Unexamined Patent Publication No. 2-42738, there has been disclosed a connecting structure in which, in a COB based packaged printed-circuit board, a flexible bonding layer is placed as a cushioning material between an IC chip and a substrate to improve the reliability of the bond. However, in the case of this prior connecting structure, it is required to provide the flexible bonding layer for exclusive use for the purpose of taking the cushioning action, which leads to higher component cost and manufacturing cost.
Accordingly, the present invention has been developed with a view to eliminating the problems which arise with the prior semiconductor device connecting structure. The object of this invention is to maintain steadily the connecting condition of a semiconductor device to a substrate only by adding an extremely simple construction.